Annular combustion chamber for dissimilar fluids in swirling flow relationship

ABSTRACT

The characteristics of thermodynamically and aerodynamically dissimilar fluids in swirling flow relationship are established and/or varied to accelerate mixing and hence combustion in the combustion zone and mixing and hence cooling of the products of combustion, in the dilution zone of an annular burner.

United States Patent 1191 Markowski ANNULAR COMBUSTION CHAMBER FOR DISSIMILAR FLUIDS IN SWIRLING FLOW RELATIONSHIP Stanley J. Markowski, East Hartford, Conn.

Assignee: United Aicraft Corporation, East Hartford, Conn.

Filed: Apr. 18, 1973 Appl. No.: 352,138

Related US. Application Data Division of Ser. No. 84,086, Oct. 26, 1970.

Inventor:

US. Cl fill/39.65, 60/3969, 60/3972 R, 431/173, 431/183, 431/354 Int. Cl. .5 F02c 3/00 Field of'search 60/3965, 39.69, 39.72 R, 60/3974 R, 39.06, 39.82 P; 431/350354, 9, 173, 182, 183, 185,349

References Cited 1 UNITED STATES PATENTS 2,773,350 12/1956 Barrett et al 60/3972 R 3,373,562 3/1968 Wormser 60/39.?2 R

2,679,137 5/1954 Probert 60/3982 P 2,885,858 5/1959 Lloyd 60/3969 X- 2,627,720 Williams et a1. 60/3965 Primary ExaminerCar1ton R. Croy1e Assistant ExaminerRobert E. Garrett Attorney, Agent, or Firm-Vernon F. Hauschild [57] ABSTRACT The characteristics of thermodynamically and aerodynamically dissimilar fluids in swirling flow relationship are established and/or varied to accelerate mixing and hence combustion in the combustion zone and mixing and hence cooling of the products of combustion, in the dilutionzone of an annular burner.

19 Claims, 49 Drawing Figures PATENTEBmzx m4 SHEET 0% HF 11 PA'TENIEUmz: m4

PATENTEDHAY 21 I974 3.811.277 sum 070F 11; I

I I n mmmmm mm 3.81 1.277

sum 10 or 11 FIC3-38 ZZZ F|(5-43 FIG.44

ANNULAR COMBUSTION CHAMBER FOR DISSIMILAR FLUIDS IN SWIRLING FLOW RELATIONSHIP This is a division of application Ser. No. 84,086, filed Oct. 26, 1970.

CROSS-REFERENCES TO RELATED APPLICATIONS This application contains subject matter related to the following two applications assigned to the same assignee:

l.- Application Ser. No. 84,087, now U.S. Pat. No.

3,701,255, filed concurrently herewith for Shortened Afterburner Construction for Turbine Engine and 2. Application Ser. No. 84,088 now U.S. PatNo.

3,675,419, filed concurrently herewith for Combustion Chamber Having Swirling Flow."

BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates to the controlled mixing of two thermodynamically and aerodynamically dissimilar flu-' idsand particularly to the use of swirling flow between two dissimilar fluids in annular combustion chambers, such as the burners and afterburners of turbine engines, to accelerate both the combustion process and the temperature reduction process of the products of combustion in the dilution zone of the burner.

2. Description of the Prior Art In the combustion chamber and burner art, it has been conventional to burn in a cylindrical chamber by discharging an atomized fuel spray into the center thereof with air being discharged therearound through a vaned cascade at tangential velocity V, so as to form a recirculation zone of the atomized 'fuel and swirling air so mixing. This recirculation zone is formed because the angular momentum of the air is proportional to the tangential velocity V, thereof times the radius of the air particle involved from the burner central axis, accord-.

ingly, any air which is at or near the burner axis is of minimal orzero radius so .that the tangential velocity attempts to go to infinity with the result that nonswirling secondary air is brought in around the recirculation zone formixing with the stagnated fuel-air mixture downstream of the recirculation zone and for cooling-the walls of the combustion chamber, as typically shown in U.S. Pat. No. 3,498,055.-

These prior art burners are called can burners, because of their cylindrical shape, or can-annular burners, because they have a series of can-shaped inlet sec- I tions opening into an annular main section. The momentum-velocity system of establishing a recirculation zone is used in the can portion of both.

The momentum-velocity system of establishing a recirculation zone does not work in an annular combustion chamber because all combustion stations are of dilution zone of an annular combustion chamber besubstantial radius and therefore I utilize the interdigitation of the swirling sheets of dissimilar fluids to perform this function.

The patents to Johnson, U.S. Pat. No. 3,030,773 and Sanborn, U.S. Pat No. 2,473,347 utilize swirling flow in combustion chambers but it will be noted that these are cylindrical or can type combustion-chambers and that none of this priorart teaches the use of establishing an unstable interface between two swirling dissimilar fluids for the purpose of accelerating mixing and combustion therebetween by the establishing and/0r control of the fluid density and tangential velocity V, to produce dissimilar product parameters pV, between the two fluids. The conventional can or cylindrical burner is shown in afterburner form in U.S. Pat. No. 2,934,894.

. combustion chamber to flow in swirling motion so as to improve combustion, however, it should be noted that in the Ferri et al. patent there is but a single swirling stream and he therefore does not achieve the mixing and accelerated combustion advantages of my invention. The patent to Meurer, U.S. Pat. No. 3,078,672 causes swirling air to be passed through a can-type burner and causes a solid sheet or film of fuel to be passed along the inner surface of. the burner outer wall to be vaporized and to burn with the swirling air at the outer wall. Combustion takes place at the interface between the air and the fuel at the outer wall of the combustion chamber and the products of combustion move inwardly to begathered'and recycled through duct 22.

Meurer clearly does not teach the concept of mixing and combusting two dissimilar fluids by control of the parameter products taught herein. My U.S. Pat. No. 3,393,516 illustrates curved flow in an exhaust gas deflector of a turbo-fan engine but itshould be noted that there is no mixing and combustion in connection with the curved flow, in fact, such would be undesirable.

SUMMARY OF THE lNVENTlON A primary object of the present invention is to provide a mixer conflguration which can be used to increase mixing between dissimilar swirling flow fluids in i the combustion zone of an annular combustion chamber to accelerate combustion by increasing the mixing rate between the cool fuel-air mixture and the hot gases and which can also be used to accelerate mixing in the tween the products of combustion and the cooling air to accelerate temperature reduction. Combustion is mixing limited. The time or burner length required to obtain complete combustion can be limited by that necessary to mix together the hot gases and the cool fuel-air mixture. Accelerated mixing in both the combustion and dilution zones will shorten the length of the combustion chamber and hence shorten thelength and weight of the engine.

A primary object of the present invention isto provide an improved annular combustion chamber by establishing, controlling and/or varying the product parameter pVf, where p is fluid density and V, is fluid tangential-velocity, between two dissimilar swirling fluids to establish an unstable interface therebetween to accelerate mixing and hence combustion in the combustion zone and mixing and hence cooling in the dilution zone of the combustion chamber.

In accordance with the present invention, this product parameter is established, controlled and/or varied so that the product parameter of the fluid which is flowing at the lesser radius about the combustion chamber axis is greater than the product parameter of the fluid which is flowing at the greater radius, so that the mixing ratio in the combustion chamber is determined by the ratio pV, (inner flow) pV, (outer flow).

In accordance with a further aspect of the present invention, the interface between two dissimilar swirling combustion chamber fluids are established or controlled so that outside-inside burning occurs in the combustion chamber.

The invention permits acceleratedmixing and combustion or accelerated mixing and dilution to occur in several annular combustion chamber configurations, for example, in the concentric flow mixer configuration, the barberpole mixer configuration, and the bent tube or folded combustion chamber mixer configuration.

In accordance with a further aspect of the present incan take place utilizing either the premixed or diffusion principle.

It accordance with a further aspect of this invention, hardware is provided to establish, control or vary the orientation of two concentric fluid streams of different thermodynamic and aerodynamic states in such a way that theproduct parameter density, p, of the inner stream times the tangential velocity V, of the inner stream is greater than the corresponding product parameter of the outer stream.

In accordance with still afurther feature of the present invention, compound mixing in radial, parallel stagingoccurs both in the combustion zone and the dilution zone of an annular combustion chamber in whichthe combustion zone and the dilution zone are axially staged in series so as to reduce the overall length of the combustion chamber and hence the engine length and weight.

In accordance with still a further feature of this invention, several modifications of the pilot combustion zone in a concentric mixer for a primary combustion zone are usable and of advantage depending upon the particular requirements of the combustion chamber configuration involved.

In accordance with still a further aspect of the present invention, triggers are used to disturb the unstable interface between two swirling streams to accelerate mixing and either combustion or cooling therebetween.

In accordance with still a further aspect of this invention, a combination flameholder and/or trigger can be used in a swirling flow annular combustion chamber to accelerate mixing and burning of the products of com-- bustion from the recirculation zone established downstream of the flameholder and the fuel-air mixture passing around the flameholder.

In accordance'with still a further feature of this invention, swirling fluid interface trigger mechanisms are provided in the form of a corrugated and tapered rings, which may have holes or scoops therein for noise deadening and trigger mechanism cooling purposes.

In accordance with still a further feature of this invention, combustion apparatus is provided in which combustion or dilution zones are located in series in which mixing occurs in both zones at parallel radial stations.

In accordance with a further teaching of this invention, the unstable interface between two swirling streams of fluid which are established by the product parameter criterion taught herein can be physically interrupted or disturbed by a variety of trigger mechanisms.

It is a further teaching of this application to establish a stable interface criteria between the cooling air for a combustion chamber liner and the products of combustion.

In accordance with still afurtherfeature of my invention, swirling flow in an annular combustion chamber invites the use of flameholders therein and the use of a substantial variety of fuel injecting devices to be used FIG. 1 is a schematic representation of two dissimilar fluids flowing in swirling relationship in separated coannular passages and then joining and mixing in a single annular passage. f

FIG. 2 .is a schematic showing in cross-section of the FIG. 1 flow representation.

FIG. 3 is a vector diagram of the fluid flowing in swirling fashion in the FIG. 1 and 2 environment and the other environments disclosed herein.

FIG. 4 is a showing of the static pressure distribution across the outer and inner swirling fluid flows of the FIG. 1 and 2 environment. I,

FIG. 5 is a schematic representation of mixing occurring in two fluid streams flowing in side-by-side relationship and which are caused to swirl in passing through a bent tube.

FIG. 6 is a schematic cross-sectional showing of a barberpole swirl mixer.

FIG. 7 is an end view taken along line 7-7 of FIG. 6;

F IG. 8 is a showing of an annular combustion chamber concentric mixer utilizing the premixed burning I principle.

FIG. 9 is similar to FIG. 8 but utilizing the diffusion burning principle.

FIG. 10 is a cross-sectional showing of an annular combustion chamber barberpole' mixer used in the combustion zone and utilizing the premixed principle.

FIG. 11 is similar to FIG. 10 but utilizing the diffusion burning'principlef I i FIG. 12 is a showing of a premixed combustor employing bent tube mixing in a folded combustion chamher which is preferably of the annular type.

FIG. 13 is a showing of a modern turbine engine'of the type used in the modern aircraft and shown utilizing my invention.

FIG. 14 is a cross-sectional showing of an annular combustion chamber using a concentric mixer in both the combustion zone and the dilution zones.

FIG. is a showing of a vane of an annular vane cascade and its actuating mechanism to make the cascade FIG. 19 is a cross-sectional showing of the vaned, he- I lical slots used in the inner wall of the dilution zone mixer of FIG. 16 and is taken along line 19-19 of FIG.

FIG. 20 is a modification of the helical slots shown in FIG. 18 and can be used in the barberpole mixer either in the combustion zone or the dilution zone of an annular combustion chamber.

FIG. 21 is a cross-sectional showing of an annular combustion chamber having axially staged combustion and dilution zones and utilizing a. concentric mixer in the combustion zone and a barberpole mixer in the dilution zone.

FIG. 22 is a cross-sectional showing of an annular combustion chamber having a conventional combustion zone and dilution zone of the folder burner or bent tube variety utilizing my invention.

FIG. 23 is a modification of the primary combustor portion of the combustion zone mixer shown in FIG. 14.

FIG. 24 is a'modification of the concentric mixer used in the combustion'zone of an annular combustion chamber which may be substituted for the type shown in FIG. 14.

FIG. 25 is an enlarged, partial, cross-sectional showing of the flameholder member taken along line 2525 of FIG. 24.

FIG. 26 is a showing of a modification of the combustor shown in FIG. 25.

FIG. 27 is an enlarged showing of the FIG. 26 construction taken along line 27 of FIG. 26.

F IG. 28 corresponds to FIG. 27 and shows the secondary flow patterns between the helical guide vanes.

FIG. 29 is still another modification for the primary combustion chamber shown in FIG. 14.

FIG. 30 is a schematic representation of two swirling fluids flowing through annular passages with a splitter duct therebetween and with a trigger mechanism attached to the downstream end of the splitter duct.

FIG. 31 is an end view of the FIG. 30 construction.

FIG. 32 is a cross-sectional showing of a trigger mechanism which may be substituted for the trigger mechanism shown in the splitter duct of FIG. 14.

FIG. 33 is a showing of the trigger mechanism of FIG. 32 shown with the splitter duct unrolled for purposes of better' illustration.

FIG. 34 shows another modification of trigger mechanism of FIG. 14.

FIG. 35 is a showing of a further trigger mechanism modification utilizing plural rows or patterns of helical slots in or near the trailing edge'of a splitter duct.

FIGS. 36 and 37 are plan and end views of still another trigger mechanism modification of the variety which utilizes both a helically slotted and helically corrugated downstream end on a splitter duct to perform their swirling fluid interface triggering functions.

FIG. 38 is a showing of still another trigger mechanism modification utilizing a combination of helical slots and scooped projections cooperating therewith at the downstream end of a splitter duct to accelerate mixing.

FIG. 39 is a representation of irregular trigger corrugation utilized for the purpose of noise suppression.

FIGS. 40 and 41 depict annular combustion chamber flow passage modifications which can be used because of the swirling flow therethrough to retard or prevent flow separation'of the boundary layers along the diffuser walls.

FIGS. 42a and 42b are showings or an annular combustion chamber utilizing swirl flow and further utilizing a compound vane cascade at the inlet thereof to control the amount of swirling at the various radial stations across the cascade so as to discourage boundary layer flow separation and permit the utilization of shortened diffuser section in the combustion chamber, thereby reducing the length of the combustion chamber.

FIGS. 43 and 44 and showings of the axial velocity profile and tangential velocity profile of the air immediately downstream of the cascade of compound vanes of FIG. 42.

FIG. 45 is a cross-sectional showing of a scoopedaperture which may be used with trigger mechanisms, such as those shown in FIG. 14.

FIGS. 46 thru 48 are showings of annular combustion chambers utilizing radially staged combustion for reduced combustion chamber and engine length and having, provisions for engine power performance control.

DESCRIPTION OF THE PREFERRED EMBODIMENT To fully explain the subject matter of this application, it is deemed'desirable to first describe the theory involved.

My observation of the dynamic behavior of concentric dissimilar swirling flows leads to the discovery of a fluid interface instability phenomenon that can be used to increase the mixing rate between the dissimilar fluids and which'therefore is of particular interest in combustion chambers to accelerate combustion by increasing the mixing rate and hence the effective flame speed and also to accelerate the mixing which takes place in the combustor dilution zone wherein the products of combustion are cooled by mixing with cooling air before being passed through the turbine. AS used herein the term dissimilar fluids means fluids which are thermodynamically and aerodynamically dissimilar. This phenomenon of interest and its characteristics will now be described by referring to FIGS. 1 and 2. In these figures, two dissimilar fluids are flowing in concentric swirling flow patterns and are isolated initially by a cylindrical separator wall 10, which is positioned between cylindrical ducts l2 and 14 so that walls l0, l2 and 14 are concentric about centerline or axis 16 and cooperate to define concentric annular passages 18 and 20. While the outer fluid will be described as the hot fluid and the inner fluid the cold fluid, this does not have to be the case. As the swirling fluids pass downstream of the separator termination point 22, interface 24 is established'therebetweenjAs best shown in FIG. 3, the

velocity of each fluid may be represented by the flow vector diagram shown where V, is axial velocity, V, is tangential velocity and V is actual velocity in the indicated direction. Fluid flowing in such a manner comes under the primary influence of two forces of significant magnitude, namely, centrifugal forces and forces due to the pressure gradient which exists in the duct through which the fluid is flowing. At a given radius, the centrifugal force, F is proportional to the mass of the fluid, and consequently the density, p, of the fluid, and the square of the tangential velocity or tangential velocity component V,, of the fluid. The pressure gradient force, F,,, is proportional to the radial pressure gradient and results from the radial difference in static pressureacross the radially projected area of the fluid element. During the passage of the two fluids through annular passages and 18, these forces are in equilibrium, as best shown in FIG. 1 with respect to simulated fluid particles 26 and 28, and the fluid flows in its helical path.

Downstream of separator 10, where both fluids enter common annular passage 30, the two fluids are in direct contact with each other and therefore are capable of influencing one another.

By viewing FIGS. 1 and 4 it should'be noted that the static pressure distribution profile 32 for the outer swirling, usually hot fluid is considerable less steep than the static pressure distribution profile 34 of the inner swirling cold fluid, and this is reflected in the magnitude of the pressure gradientforce, F indicated to be acting upon the outer stream element 28 and the inner stream element 26 in FIG. 1. These pressure gradient forces acting on elements'28 and 26 are balanced by the centrifugal force, F action thereon because of the radial equilibrium of each individual stream.

By study and observations have lead me to the discovery that interface 24 between these two dissimilar fluids is unstable if the product parameter pVfi, i.e., the product of the fluid density p and the square of the tan gential velocity V, of the fluid, of the outer radial fluid is less than that of inner radial fluid. This instability is demonstrated by introducing a disturbance into the interface 24 suchthat a local interface convolution 36 projects radially outwardly into the outer radius fluid region. The element offluid 26' in this projection 36 is exposed to the relatively small radial pressure gradient, F to'the outer radius fluid region but still retains its high centrifugal force, F This establishes an unbalance of forces on element 26' and results in an acceleration of the disturbance radially outward to cause the convolution size and penetration into the outer radius fluid to increase, thereby increasing the rateof mixing between the two fluids. In similar fashion, a convolution 38 of the interface 24 projecting radially inward will result in a force unbalance on fluid element 28' which remains under the relatively small centrifugal force, F and comes under the influence-of the substantially larger pressure gradient force, F and is consequently accelerated radially inward to result in rapid inward growth of convolution 38 and accelerated mixing between the two streams.

The relative magnitude of the unbalanced forces just described may be assessed by considering the outer bustor pilot will change relatively to a smaller magnitude, the unbalanced force is seen to be three-quarters or more of the maximum centrifugal force on the two fluids. This magnitude of the unbalanced force is decidedly first order and represents a large acceleration potential available to expedite the radial movement of the two concentric fluids into a helical sheet mode-of flow.

My invention is the utilization of this phenomenon in accelerating mixing between two dissimilar swirling fluids in annular combustion chambers of the type used in turbine engines to both accelerate combustion and accelerate the dilution of the hot products of combustion with cooling air before passage through the turbine.

While I have described this mixing phenomenon in FIGS. 1 and 2 in the context of coannular, dissimilar, swirling streams, it should be borne in mind that the same mixing acceleration can be achieved in other environments such as the bent tube environment shown in FIG. 5 wherein both dissimilar streams flow through duct 66 which includes a straight portion 68 and bent portion 70, which has center of curvature 79, and' which has splitter or separation member 72 at its upstream end cooperating with duct 66 to define two passages 74 and 76 through which the two dissimilar streams flow with the fluid in the outer passage 74 having lower v; than the fluid in the inner passage 76 so that when the two fluids join in passage 78 they establish the unstable interface and accelerate mixing described in connection with FIGS. 1 and 2 as they become concentric swirling streams upon entering bent tube section 70, in view of the fact that the product parameter relationship p V -,p, V where p,, and p are the density of the hot outer, swirling stream and the cold, inner, swirling stream respectively, and V and V are their respective tangential velocities,.which are actually their through-flow velocities in the bent tube construction.

This accelerated mixing can also be established by use of the barberpole swirI mixer 80 shown in FIGS. 6 and 7. The term barberpole" is selected to describe this mixer because it causes the two dissimilar fluids to form into a series of interdigitated, swirling sheets. or fingers. This mixer consists of outer wall 82 and inner wall 84 which preferably diverge to form diverging passages 86 through which the swirling main fluids flow and which have selectively oriented helical slots 88 and 90 extending, therethrough, respectively, through which the secondary fluids flow and are caused to enter parallel to the main stream flow. As best shown in FIG. 7 the direction of helical slots 88 and 90 are such that they are locally parallel to the direction of the swirling main flow. By use of appropriate guide vanes and inlet conditions for the secondary flows the product parameter flow criterian: pV, inner secondary pV, main flow and pVP outer secondary pV, main flow are attained. With this flow criteria the sheets of secondary flow will penetrate rapidly across the main flow because the same mixing phenomenon previously described in connection with the FIG. 1 and 2 construction occurs here between each swirling fluid sheet and the two swirling sheets of dissimilar fluids adjacent thereto. Accordingly, total required mixing will occur more rapidly. In certain situations, it may be desirable to use a barberpole mixer of the type shown in FIGS. 6 and 7 in which the helical slots are used in one of the walls 82, or 84 only. In the FIG. 6 and 7 barberpole construction, the main flow is preferably hot air and the secondary flows are cooler air and the slots 88 and 90 are oriented to bring about not only helical flow but helical flow substantially parallel to the main flow direction.

Any of these mixers, that is, the concentric mixer, barberpole mixer and the bent tube mixer can be effectively utilized in the combustion zone of a combustor or burner to increase the rate of mixing and hence rate of combustion and effective flame speed so as to reduce overall burner length as illustrated in FIGS. 842. To emphasize similarity of function the reference numerals of FIGS. 1, 2,6 and 7 will be repeated in describing the FIGS. 8-12 constructions.

In practice when using these mixers in the combustion zone of a combustor, one of the swirling streams is used as a hot pilot to initiate combustion in-the other swirling stream, which is a fuel-air mixture. Burning occurs when the two streams mix.

We will now consider which stream to selectas the pilot stream.

In the case of the concentric mixers and combustion chambers shown in FIGS. 8 and 9 and the bent tube combustion chamber shown in FIG. 12, it is apparent that the pilot stream should be the outer stream because the density depression caused by heating helps in inner pV, outer. In the barberpole mixers and combustors shown in FIGS. 10 and 11, the choice of which stream will act as the heated pilot is not as obvious. In view of the density depression associated with fluid heating, it is apparent that the pilot stream should be one of the streams requiring a low pV, product parameter and hence the pilot stream should not be the secondary flow in inner passage 114. The main stream 112 should be chosen as the pilot stream to avoid the severe wall cooling problems which would be caused by injecting a hot gas secondary stream from passage 112 along outer walls 82. In view of the low density of the pilot stream, the product parameter pV, for the outer secondary fluid can be made smaller than the product pa-- rameter pV, of the pilot to obtain the desired rapid mixing by permitting little or no tangential velocity V, as it passes through slots 88. The desired interface instability criteria between the pilot flow from passage 112 and inner secondary flow from passage 1 14 is satisfled by the use of the required turning vanes or the like to adjust the tangential velocity (V,) level to satisfy the required criteria pV inner pV, pilot. Of course, the combustion'process in the pilot decreases the density of this stream thereby assisting in satisfying this criteria.

FIG. 8 depicts a concentric mixer in a combustion chamber combustion zone where concentric passages 18 and 20 are formed between concentric ducts 12,- 10 and 14 and wherein splitter duct 10 terminates short of the outer ducts so that the outer ducts form' combustion zone downstream thereof. Appropriately positioned inlet guide vanes or other mechanisms cause swirling fluid to pass through each of passages 18 and 20. The flow in passage 20 serves as the pilot combustion stream in that pilot fuel is injected thereinto through pilot fuel nozzle mechanism 92 which sprays atomized fuel into the fluid passing therethrough just upstream of flameholder 94 to form pilot combustion zone 96 downstream thereof wherein the fuel-air mixture is burned and vitiated after appropriate ignition in comtangential velocity squared pV, is greater than the corresponding product parameter for the outer swirling pilot stream of passage 20 so that accelerated mixing and subsequent combustion takes place between the two fluids in combustion zone 30. The burner shown in FIG. 8 utilizes the premixed burning principle in that fuel is sprayed into the secondary stream 18 prior to entering the mixing and combustion zone 30 and this stream becomes a combustible fuel-air mixture that is subsequently ignited and vitiated when it is mixed with the hot pilot gases or flame from stream 20.

Such a concentric mixer used as'a combustor utilizing the diffusion burning principle is shown in FIG. 9. The diffusion burning technique works on a different principle than the premixed burning technique. In the I diffusion burning technique, the pilot fuel from nozzle 92 is fully combusted and fully vitiated in pilot combustion zone 96 such that little or no oxygen remains therein and, accordingly, any fuel added thereto downstream of fully vitiated interface 100 can be vaporized only by the hot products of combustion from pilot zone 96. This phenomenon is taken advantage of in the diffusion burning principle andsecondary fuel is discharged into stream 20 by secondary fuel nozzles 101 but this secondary fuel cannot burn until it is mixed with the secondary air being passed in swirl fashion through in stream 18. In this case it will be seen'that no fuel whatsoever is directed into stream 18 and that the pilot stream 20 carries not only the heat necessary to initiate combustion and mixing in mixing and combustion zone 20 but also carries the fuel to support this combustion process, when mixed with the air from passage 18. 4

' FIGS. 10 and 11 depict barberpole mixers of the type shown in FIGS. 6 and 7 utilized to form combustion chambers of the premixed burning and diffusion burning variety. In the FIG. 10 construction, ducts 102, 104, 106 and 108 are positioned concentrically about center line 16 to form coannular passagesl10, 112 and 114 therebetween. Guide vanes or the like are used to produce swirling flow in passages 110, 112, and 114 to achieve the desired tangential velocity V, or, as in all other configurations disclosed, this flow may be accepted directly from a compressor which does not have straightening vanes at its outlet. Ducts 104 and 106 join walls82 and 84 which define passage 86, which is' preferably divergent and is the main combustion zone 60. Fuel is sprayed through pilot nozzles 92 into annular passage 112 to be combusted in pilot combustion zone 96 downstream of flameholder 94 to serve as the pilot stream. Secondary fuel is injected into passages flow substantially parallel to the swirling pilot stream being directed from pilot combustion chamber 96 for accelerated mixing and subsequent combustion with the pilot stream in mixing and combustion zone 60. As

in the case of the barberpole mixer, the direction of flow of the secondary fuel-air mixture through slots 88 and 90 are adjusted by suitable guide vanes to satisfy the instability criteria V, outer secondary pV, pilot and pV, inner secondary pV, pilot.

In the FIG. -11 construction, all air entering passage 96 enters with a selectively established tangential velocity V,. This spinning of the air will lower the static pressure in the pilot combustion chamber 96. The premixed fuel-air mixture passing at a larger radius through passage 110 does not necessarily have swirl added thereto. In passage 110 air enters the combustion zone ,60 through slots or helical hole pattern 88 in wall 82, such holes 88 are helical in nature or holes or slots designed in helical pattern. This air will accelerate radially through the holes 88 due to the static pressure drop across the holes or slots and once inside primary or pilot combustion zone 60, this air will continue to be accelerated radially inward because of the radial pressure gradient established by the swirling pilot fluid from passage 96 in combustion chamber 86. By admitting this fuel-air mixture through helical slots or holes or slots in a helical pattern, 88, a very rapid combustion pattem'of helical layers will be established in the main combustion zone 60. The fuel-air mixture layers thus formed are burned as interdigitated mixing with the swirling air from the pilot proceeds. As the fuel-air mixture through slot 88 ,is burned, its radial inward motion is locally further accelerated because the consequent decrease in the density lowers its pV, product parameter even further and the radial pressure gradient will accelerate a small portion of burned gas faster than unburned gas. The portion of the fuel-air mixture which passed through helical slots or hole pattern 90 has a tangential velocity V, imparted thereto that is sufficiently high for pV pV, of the vitiated pilot gases. Therefore the admitted fuel-air mixture will form helical sheets which will interdigitate with the hot spinning air entering zone 60 from the pilot region 96 and be accelerated radially outward. Whi le the density, p, of the locally burned surface layer of the swirling fuel-air mixture streams will decreasesubstantially during burning, it will retain the same tangential velocity, V since its angular momentum is unaffected by the change of thermodynamic state. Consequently, the local pV, product will be substantially reduced and its acceleration due to the radial pressure gradient will also be reduced as the I sheet burns. However, the unburned portion of the helical layer will continue to be accelerated radially outward, thus continuing .to stir the flame frontv until it is completely burned. I Viewing FIG. 11 we see the barberpole mixer used as a combustion chamber utilizing diffusion .burning in which concentric, preferably cylindrical ducts 102, 104, 106'and 108 are positioned concentrically about center liner axis 16 to'form coannular passages 110, 112, and 114 therebetween, with ducts 104, 106 extending into preferably divergent walls 82 and 84 to form section 86-which defines the main combustion zone 60. Pilot fuel'from nozzles 92 is admitted in atomized form to passage 1l2upstream flameholder 94 to be fully conbusted and vitiated-in pilot combustion chamber 96 so that theproducts of combustion are fully vitiated upstream at interface 100. Secondary fuel is admitted to annular passage'llZ downstream of interface 100 through secondary fuel nozzle 101 to be heated and carried with swirling combustion products of the pilot combustionchamber 96 into combustion zone 60, secondary air is passed through annular ducts 110 and 114 and through opposed helical slots 88 and 90, respectively, into mixing and combustion chamber 60 to be mixed with, the hot, fuel rich, flow from pilot stream duct 112. As the mixing process proceeds the excess fuel in the pilot stream comes into contact with the sheets of secondary air entering through slots 88 and 90 and combustion occurs at the multiplicity of interface between these flows.

FIG. 12 depicts a bent tube mixer in the form of a folded burner or combustor of the premixed burning variety. In the FIG. 12 premixed burning configuration, the first fluid is passed through passage 74 to have atomized fuel added thereto from pilot fuel nozzle 92 and so that a pilot combustion zone is established at 96 so as to provide an outer pilot stream entering the curved section of curved duct 66 to serve as a pilot to institute mixing with and subsequent combustion of the fuel-air mixture being introduced through passage 76 into mixing and combustion chamber 30. The fuel-air mixture in passage 76 is generated by the passage of fluid therethrough and the introduction of atomized fuel thereinto through secondary fuel spray nozzles 98. It will accordingly be seen in the FIG. 12 construction that a hot pilot stream is established as the outer swirling stream with respect to the inner colder fuel-air mixture stream, both of which are concentric about center of curvature 79 to cause accelerated mixing and combustion therein in view of the flow criteria pV, inner pV, outer. Itwill be evident to those skilled in the art that the construction shown in FIG. 12 could be made of the diffusion variety by moving pilot fuel'nozzle 92 and flameholders 94 farther upstream so that combustion in the pilot combustion zone 96 is 'comswirling flows in the concentric and bent tube mixers,

it is sometimes desirable to use trigger mechanisms at the end of ducts which serve as splitter ducts between theswirling flow of two different fluids, such as triggers 164 and 166 shown in FIG. 14, to physically disturb the interface between the swirling fluids. A discussion of the theory of operation of these trigger mechanisms is believed to be helpful at this point and reference is first made to FIGS. 30 and 31 in this regard. In FIG. 30 we see trigger mechanism 166 positioned at the downstream end of splitter duct 246 which is of circular cross section and positioned concentrically about axis 16 and cooperates with outercylindrical duct 248 and inner cylindrical duct 250 to define outer annular gas passage 252 and inner annular gas-passage 254. For purposes of illustration, it should be considered that a hot fluid, which is to be the pilot fluid, is passed through passage 252. This hot outer fluid has a density p,, and a tangential velocity V,,,. Asecond fluid, which is preferably a cold (high density) combustible mixture, I

is passed through inner annular passage 254 and has a density of p and a tangential velocity V To effect accelerated mixing between these two fluids of passage 252 and 256, it is essential that the mixing criteria p p VJ exists to establish an unstable interface between two swirling fluids. Above and beyond this, the use of trigger 166, which is shown to be a convoluted sheet metal ring member attached to the downstream end of splitter duct 246 further serves to accelerate mixing and combustion. Trigger 166 defines convolutions which follow helical paths growing in amplitude in a downstream direction and as the fluids of passage 252 and 254 pass thereover, a regular pattern of radial fluid motion will be initiated outwardly and inwardly due to the change of flow direction imparted to the fluids by trigger mechanism 166. The motion thus initiated will grow because of the instability'of the interface. Such a trigger mixer has been successfully demonstrated using air at 200 Fahrenheit and 800 Fahrenheit as working media.

The amount of tangential mixing induced by fluid shearing at the helical sheet interface will depend'upon the difference between the circulation per radian of the fluids in ducts 252 and 254.

The use of trigger mechanisms provides the advantage of controlling the location, size and shape of the disturbance at the interface between the two fluids and it will be appreciatedthat in constructions where trigger mechanisms are not used the disturbance of the interface is caused by turbulence only and is therefore random in nature.

Of particular interest is a piloted combustion application of such a triggered inside-out mixing configuration as shown in FIGS. 30 and 31. Here, the hot vitiated pilot flow would be the outer radius fluid having a low pV, product parameter, while the cold combustible mixture would be the inner radius fluid having a high pV, product parameter. FIG. 31 is a showing of the combustion-pilot primary combustion zone downstream of trigger 166. The flame front where active combustion occurs is located at the interface 255 and 253, respectively, of the triggered helical sheets of hot pilot flow from duct 252 and cold combustible mixture flow from duct 254. As shown in FIG. 31, the flame speed, F/S, moves against the trigger helical current of the combustible mixture flowing radially outward and into the hot mass of pilot flow. As the combustion occurs at the flame front, elements of air undergo an abrupt density change in a high centrifugal field with resultant release of the acceleration potentialto magnify the local turbulence and effective flame speed. This local stirring action, i.e., increased turbulence, is superimposed upon the interface of the triggered mixing of the initial hot pilot and cold combustible mixture flows. The triggered hot pilot gas from passage 252, which comprises a radially inward directed current, has an interface flame speed that moves with the current, as well as laterally into the unburned mixture. Again, the local magnitude of turbulence is increased at the flame front by the abrupt fluid density changes in a strong centrifugal field which increases the effective flame speed. The difference in circulation per radian for the initial hot pilot flow and cold combustible mixture provides a superimposed tangential mixing through tangential shearing action.

Another trigger mechanism, which could be used as a substitute for trigger 166 in the FIG. 14 and 30 construction, is shown in FIGS. 32 and 33. As shown in FIG. 32,.splitter duct 246 and ducts 248 and 250 are used in the same fashion as in the FIG. 30 construction. Hot products of combustion flow between ducts 246 and 248, while the cooler fluid, such as a fuel-air mixture, flows in the passage between ducts 246 and 250. Trigger mechanism 258 is located at the downstream end of splitter duct 140 and consists of a series of oppositely oriented vane 260 and 262 pairs forming vortex generators which are spaced circumferentially about splitter duct and extending radially outwardly from the splitter duct and in any desired number of axially spaced rows. Once again, it is the object of trigger mechanism 258 to convolute the interface between the hot products of combustion flowing on one side of splitter duct and the cooling air or fuel-air mixture flowing in passage 130 on the other side of the splitter duct so as to take advantage of the mixing criteria in that the pV, product parameter of the hot gases flowing at the greater radius is less than the pV, product parameter of the cold air or fuel-air mixture flowing at a lesser radian at the interface therebetween and any convolution will react with the respective pressure gradients in the hot and cold regions to cause radial mixing currents with cold air currents moving into the hot flow in helical sheets and the hot fluid currents moving into the cold region in helical sheets. The flow at the interface downstream of the trigger plane is unstable and the trigger configuration establishes the helical sheet mixing patterns. This mixing occurs from the inside (minimum radial station) to the outside (maximum radial station) and shortens the length of the combustion chamber and engine by accelerating the mixing process.

Referring to FIG. 34 we see still another modification of a splitter duct trigger which could be used in place of trigger 166 of FIG. 14. The trigger of FIG. 34 consists of a series of helically oriented and circumferentially positioned slots 260 at the downstream end of splitter duct 140. The slots are preferably oriented to be parallel to the direction of flow, V, of either the hot or cold gas streams and serves to trigger or disturb the unstable interface which exists between the swirling hot gas flow from the combustion chamber flowing outside splitter duct and the swirling colder air of the cooling gas stream flowing inside of the splitter duct 140 so as to accelerate intermixing.

An additional trigger embodiment is shown in FIG. 35 wherein a plurality of helically extending and circumferentially positioned slots 262 are positioned forward or upstream of slots 260 of the type shown in FIG. 34. Thereby adding to the mixing advantage of the trigger device by utilizing plural slot rows and/or patterns.

Still a further trigger configuration is shown inFlGS. 36 and 37 wherein slots comparable to slot 260 of FIG. 34 are fabricated so as to be elongated and are circumferentially positioned helical slots 264. In this configuration, the after end of splitter duct 140 is fabricated, as shown in FIG. 37, to be corrugated in shape so that the FIG. 36 and 37 trigger is a combination of the slotted trigger of FIG. 34 and the convoluted trigger of FIG. 30.

Still another form of trigger is shown in FIG. 38 wherein scoops 266 are added to helical slots 268, which are comparable to slots 260 of FIGS. 34 and 35 and which serve to scoop the cold spinning air from a construction comparable to the FIG. 14 construction flowing on the outside of splitter 140 into the hot region radially inward of the splitter duct 140 where the products of combustion from combustion chamber 60 flow, thus triggering the mixing pattern downstream of the splitter duct plane. This FIG. 38 construction will set up helical spinning layers of hot and cold air to mix downstream of the splitter duct. While but a single row of such scooped slots are shown in FIG. 38, it should be realized that more than one row or a pattern thereof could be used, as is shown in FIG. 35 without scoops. For improved acoustic properties and for improved combustion of the trigger 166, it is recommended that trigger 166 be made of sheet metalwith a series of small holes 257 therein and preferably, scoop member 259 (see FIGVSS) to be' associated with holes 257 to 7 force small jets from the cold side of the trigger to flow to the hot side to cool the trigger and to also introduce a fine scale of disturbance or turbulence to improve combustion.

As mentioned previously, acoustic benefit can be I gained by utilizing perforations in the corrugated trigger of the type shown in FIG. 50 and this is important because large amplitude noise has been shown to affect combustion efficiency adversely. Additional noise suppression can be achieved by varying the height and width (distance between) of the trigger corrugations or other trigger mechanisms, and also varying the cycle of the trigger pattern peripherally to achieve noise suppression, thus producingspiraling or helical sheets of hotand cold gases having different frequency response. Such a configuration is depicted in FIG. 39 wherein h represents height or amplitude of the convolutions and l and m represent different corrugation widths.

An engine of the type in which my inventionmay be "used is shown in FIG. 13 as turbine engine 40, which consists of a compressor section '42, a burner or combustion section 44, a turbine section 46, and may have an afterbumer section 48, which terminates in a variable area nozzle 50. Engine 40 is preferably of circular cross-section and concentric about axis 52. Combus- 4 tion section 44 includes outer casing 54 and and annular combustor combustion chamber 56, which consists of diffuser inlet section 58 combustion zone 60 and dilution zone 62. As used herein, the term fannular combustion chamber means a combustion chamber having an annularpassage extending from the inlet, or upstream end, to the outlet, or downstream end thereof. Fuel is supplied to cornbustor 56 by variable output fuel pump 64 which is either under pilot manual or pilot set automatic control, and-is fed into the inlet of combustor 56 in a fashion to be described hereinafter, to be mixed therewith with a portion of the pressurized gas from compressorsection 42 to form a combustible fuel-air mixture to be burned in combustion zone 60,

from which the products of combustion pass into dilution zone 62 for mixing with dilutant cooling air also from the compressor to lower the temperature thereof prior to entry into turbine section 46. Engine 40 may be of the type more fully described in US. Pat. Nos. 2,747,367, 2,711,63l and 2,846,841.

A typical combustor system or section 44 of a turbine engine of the type shown in FIG. 13 may be considered tures, barberpole mixers, and bent tube mixers, can be used to perform the combustion zone region mixing and combustion function and the dilution zone region mixing and cooling functions of such a combustion section 44.

Referring to FIG. 14 we see annular combustion chamber 56 which comprises outer case 54 and inner case 113, which are preferably of circular cross-section and mounted concentrically about axis or center line 16. The air from the compressor section 42 of FIG. 13 enters annular inlet 114 in either swirling flow or nonswirling flow depending upon the discharge conditions from the compressor section 42, and portions thereof pass through pilot passage 124, main combustion zone fuel preparation passage 126 and the dilutant air pas-' sage 130. Further quantities of air flow through passages 122 and 132 to provide for cooling the walls of the combustor chamber. Vanes 116, 118, and 128 are employed as required to swirl or straighten the flow in the respective passage so as to satisfy the previously defined mixing instability criteria. Each of the passages 122, 124, 126, 130 and 132 are of annular shape since the outer burner liner 134, the innerburner liner 136 and splitter ducts 138 and 140 are of circular crosssection and concentric about axis 16. Turning vanes 116 and 118, 120 and 128 may be fixed or any or all vanes could be of the variable angle type as shown, for example, in FIG. 15 wherein each of vanes 116 is pivotally connected to duct 134 and outer housing 54 by pivot pins 144 and 146, respectively. Pivot pin 146 extends through outer case 54 and carries ring'gear 148 at its outer end, which engages circumferentially rotatable ring or annular gear 150, which is pilot operated to rotate circumferentially about axis 16 by motion of pilot actuated lever 152 into and out of this plane of the paper, thereby causing vanes 116 to rotate in unison and thereby vary the tangential velocity V, of the gas or fluid passing thereby. The swirling air which entered passage 124 has atomized fuel added thereto by fuel injection device l56 to form afuel-air mixture which is ignited by ignitor 158 and vitiated in pilot combustion chamber 160 which is located downstream of aperturetype flameholder 161', which is a tilted and apertured plate extending between ducts 134 and 138. The hot swirling stream emerging from passage 124 serves as a pilot stream for combustion chamber 60. The swirling air entering passage 126 has atomized fuel added thereto by injection member 162 and the amount of fuel to be discharged into passage 124 and 126 can be regulated by the size and number of fuel nozzles, such as 162 located therein and by pilot controlled valves 163 and 165 located in the fuel line thereto. The atomized fuel entering passage 126 mixes with the swirling gas passing therethrough to provide a combustible fuelair mixture to combustion chamber 60 for accelerated mixing pilot stream emerging from passage 124 andsubsequent combustion of this flow. It will accordingly 

1. In an annular combustion chamber, means to establish compound radially staged mixing comprising: A. means to establish swirling flow pattern of a first fluid of product parameter Rho 1 Vt12 where Rho 1 is the fluid density and Vt1 is the tangential velocity of the swirl motion in a central portion of the combustion chamber, B. means to establish a swirling flow pattern of a second fluid of density Rho 2 and a tangential velocity Vt2 of selected product parameter Rho 2 Vt22 radially inward of and in interface engagement with the first fluid flow so that the Rho Vt2 product parameter of the second fluid being greater than that of the first fluid to accelerate mixing therebetween and, C. means to establish a swirling flow pattern of a third fluid of density Rho 3 and tangential velocity Vt3 radially outward of the first fluid and in interface engagement therewith and having a product parameter Rho 3 Vt2 less than the Rho 1 Vt12 product parameter of the first fluid to accelerate mixing therebetween.
 2. Apparatus according to claim 1 including means to add fuel to said first, second and third fluids to create a first, second and third fuel-air mixture, respectively, and means to ignite said first fuel-air mixture to serve as a pilot for said second and third fuel-air mixtures.
 2. a second duct surrounding said axis and position within said first duct to cooperate therewith to define a first annular passage therebetween,
 2. a third duct positioned concentrically about said axis and enveloping said first and second ducts and cooperating with said first duct to dfine a first fuel preparation annular passage therebetween,
 3. a fourth duct positioned concentrically about said axis and within said first and second ducts and cooperating with said second duct to define a second fuel preparation annular passage therebetween,
 3. a third duct surrounding said axis and positioned within said second duct and cooperating therewith to define a second annular passage therebetween and extending farther downstream in said combustion chamber than said second duct,
 3. Apparatus according to claim 1 wherein said first fluid is a fuel-rich, vitiated mixture and wherein said second and third fluids are air.
 4. An annular burner concentric about an axis and having a combustion zone and a dilution zone in series therein, A. a compound, concentric mixer with radial stage combustion in said combustion zone including:
 4. a fourth duct enveloping said axis and positioned within said third duct and cooperating therewith to define a third annular passage therebetween and extending farther downstream than said third duct,
 4. means to establish an annular combustion pilot in said pilot combustion zone,
 5. means to pass a swirling fuel-air mixture through said first fuel preparation annular passage to mix with, be ignited by, and to burn with the products of combustion from the pilot zone in said main combustion zone,
 5. means to establish swirling combustion in said first annular passage to serve as a first pilot flame,
 5. Apparatus according to claim 4 and including means to cool the products of combustion in said dilution zone.
 6. Apparatus according to claim 4 and including trigger mechanism located at the downstream end of at least one of said second, third and fourth ducts to physically disturb the interface between the swirling fluids flowing on opposite radial sides thereof.
 6. means to pass a swirling fuel-air mixture through said second annular passage to mix with and be ignited by and burn with said pilot flame and to produce a second pilot flame extending downstream thereof,
 6. means to pass a swirling fuel-air mixture through said second fuel preparation annular passage to mix with, be ignited by, and combust with the products of combustion of thE pilot flame in the main combustion zone, and
 7. wherein the product parameter Rho Vt2 of the fluid passing through the second annular passage is greater than the corresponding product parameter Rho Vt2 of the pilot products of combustion, which is in turn greater than the corresponding product parameter Rho Vt2 of the fluid passing through the said first annular passage, where Rho is density of the fluid and Vt is tangential velocity of the fluid.
 7. means to pass a swirling fuel-fluid mixture through said third annular passage to mix with, be ignited by and burn with said second pilot flame to thereby provide a concentric mixer with radial staged combustion, and
 7. Apparatus according to claim 4 and including means to pass cooling air into said dilution zone as swirling flow and passing immediately radially inboard of said fourth duct and so that the product parameter Rho Vt2 of the cooling air is greater than the product Rho Vt2 of the products of combustion from the third annular passage to accelerate intermixing and cooling therebetween, where Rho is density and Vt is tangential velocity.
 8. Apparatus according to claim 4 and including means to selectively establish combustion in said first annular passage, means to selectively establish combustion in said first and second annular passages, means to selectively establish combustion in said first, second and third annular passages.
 8. wherein the products of combustion of the first pilot flame are of density Rho 1 and rotating at tangential velocity Vt1, and wherein the fueL-air mixture flowing through said second annular passage is of density Rho 2 and tangential velocity Vt22 so that the relationship therebetween is such as to satisfy the product parameter ratio Rho 2 Vt22 > Rho 1 Vt12, and wherein the products of combustion of said second pilot flame have a density Rho 3 and a tangential velocity Vt3, further wherein the fuel-air mixture being passed through said third annular passage has a density Rho 4 and a tangential velocity Vt4 which bear a relationship to the characteristics of the second pilot flame to satisfy the product parameter ratio Rho 4 Vt42 > Rho 3 Vt32, where Rho is density and Vt is tangential velocity.
 9. An annular combustion chamber concentric about an axis and having a main combustion zone positioned axially forward of a dilution zone and including a concentric mixer with radial staging forming part of the main combustion zone and including: A. means to establish an annular pilot combustion zone positioned concentrically about said axis, B. at least two ducts of substantially circular cross section positioned concentrically about said axis within said annular pilot combustion zone and with each smaller diameter duct extending farther downstream axially than the duct outboard thereof so as to form a first annular passage between the pilot zone forming means and the radially outer duct and a second annular passage between the radially outer duct and the radially inner duct, C. means to pass a swirling fuel-air mixture through said first annular passage to mix with, be ignited by, and burn with the products of combustion from the pilot combustion zone to thereby establish a second pilot combustion zone from the products of combustion thereof, D. means to pass a swirling fuel-air mixture through said second annular passage to mix with, be ignited by and to burn with the products of combustion of the second pilot combustion zone, and E. wherein the product parameter Rho Vt2 of the swirling fluid passing through each annular passage decreases from the radially innermost passage to the radially outermost passage, where Rho is fluid density and Vt is fluid tangential velocity.
 10. Apparatus according to claim 9 and including trigger means located at the downstream end of at least one of said ducts.
 11. An annular combustion chamber concentric about an axis and having a combustion zone and a dilution zone positioned axially therewithin, said combustion zone including: A. a compound concentric mixer with radial staging including:
 12. Apparatus according to claim 11 and including trigger means located at the downstream end of the duct separating each pilot combustion zone from the adjacent other alternate passage to physically disturb the interface between the swirling fluids passing on opposite radial sides thereof to accelerate mixing therebetween.
 13. An annular combustion chamber having an axis and main combustion zone positioned axially forward of a dilution zone and wherein the combustion zone includes: A. a compound concentric mixer with plural radial staged combustion including:
 14. Apparatus according to claim 13 and including means to trigger the interface between the products of combustion of the pilot combustion zone and fuel-air mixture from said annular fuel-air passage.
 15. An annular combustion chamber concentric about an axis and having a main combustion zone positioned forward of a dilution zone and including: A. a compound concentric mixer positioned forward of the combustion zone and adapted to accomplish combustion in radial staging and including:
 16. Apparatus according to claim 15 and including trigger means located at the downstream end of said first and second ducts to physically displace the interface between the pilot products of combustion and the swirling fluids of the first and second fuel preparation annular passages, respectively.
 17. Apparatus according to claim 15 and including means to dilute and cool the products of combustion in the main combustion zone in said dilution zone.
 18. An annular combustion chamber concentric about an axis and including a main combustion zone located forward of the dilution zone and wherein the main combustion zone has a concentric mixer including: A. means establishing an annular pilot combustion zone flame, B. means for passing a swirling fuel-air mixture along said axis and immediately radially outboard and inboard of said annular pilot flame to mix with, be ignited by, and to burn with said pilot flame in said main combustion zone, and C. wherein the product parameter Rho Vt2 of the radially innermost fuel-air mixture is greater than the corresponding product parameter Rho Vt2 of the pilot flame, which is in turn greater than the corresponding product parameter Rho Vt2 of the radially outer fuel-air mixture, where Rho is fluid density and Vt is fluid tangential velocity.
 19. Apparatus according to claim 18 and including means to physically disturb the interface between said pilot flame and at least one of said fuel-air mixtures. 